is 27" tall for a lab? Briona is 27" at the shoulder and to me she seems average size.

Yeah...

From AKC:

Labrador Retriever: Size--The height at the withers for a dog is 22½ to 24½ inches; for a bitch is 21½ to 23½ inches. Any variance greater than ½ inch above or below these heights is a disqualification. Approximate weight of dogs and bitches in working condition: dogs 65 to 80 pounds; bitches 55 to 70 pounds.